Molding composition containing phenolformaldehyde and rubber



MOLDING COMPOSITION CONTAININ G PHENOL- FORMALDEHYDE AND RUBBER Carlton A. Richie, Toledo, Ohio, assignor to Owens- Illinois Glass Company, a corporation of Ohio No Drawing. Application July 26, 1957 Serial No. 674,310

5 Claims. (Cl. 260-172) This invention relates to plastics and particularly to a molding composition for plastic closures such as are applied to glass containers.

In one method of manufacture of plastic closures for glass containers, a charge of plastic material in granular form is placed in a mold and the molded closure is formed by the application of heat and pressure. Among the more commonly used compositions are those containing a resin of the phenol-formaldehyde type to which are added fillers such as woodflour, coloring agents such as carbon black, and mold lubricating agents such as calcium or zinc stearate.

In molding compositions intended for use in the manufacture of plastic closures for glass containers, certain basic requirements must be fulfilled. The molding composition must be capable of being molded satisfactorily and should not require extensive periods of retention in the mold in order to eifect cure ofthe resin. In addition, the composition should not stain the mold or be such that it easily flashes and creates waste on the article. In addition to these molding requirements, the resultant plastic closure must have suflicient impact resistance, resilience, dimensional stability, torque strength and must satisfactorily pass the bleed test, as hereinafter described.

It is therefore an object of this invention to provide an improved composition containing resin of the phenolformaldehyde type for the manufacture of plastic closures such as are applied to glass containers.

Basically, the improved composition comprises a mixture of phenolic resin, a filler such as woodflour, and a vulcanized synthetic rubber composition of the butadiene-styrene type, more commonly known as Buna-S or GRS. I have determined that the most satisfactory results may be obtained by using a rubber composition of the GRS type containing sulfur wherein the ratio of the amount of sulfur to the amount of rubber is less than approximately 50%. The most satisfactory results have been obtained when the ratio of rubber composition to filler is less than 2:5. The beneficial results appear to be generally lost when the ratio of rubber composition to filler is less than 1:5.

According to my experiments a plastic composition containing phenolic resin, a filler such as woodflour, and a vulcanized synthetic rubber composition of the GRS type may be satisfactorily molded with a minimum of cure time required, without staining the molds. The resultant closure has improved impact resistance, resilience and dimensional stability. In addition a plastic closure made from this composition satisfactorily passes the bleed test.

- Vulcanized rubber dust compositions The vulcanized synthetic rubber compositions containing rubber and sulfur which have been found to be satifactory in molding compositions for plastic closures have the following compositions:

2,867,589 Patented Jan. 6, 1959 I II III IV V Percent Percent Percent Percent Percent 'Rubber (GRS) 68-70 12-17 18-20 40 65 Sulfur 30 8-9 8 16 27 Ash content 1 1-2 1045 28-35 8-11 3-4 Oombustlbles 72 1 Determined by analysis using ASTM Standards on Rubber Products Designation D-297-T, page 145.

Molding compositions Among the molding compositions containing vulcanized synthetic rubber, which have been found to be satisfactory for manufacturing plastic closures, are the fol- Impact resistance Plastic closures made from the improved molding compositions have been found to show increased impact resistance when subjected to impact tests. For example in a test wherein a pendulum or hammer is dropped against plastic caps at increasing angles of swing, the

following results were achieved:

Impact test [10 tested each trial] Standard pheno- Amt. lie 48% resin 48% of fall Comp. B Comp. D Comp. E woodflour 50..- OK OK 0K a. 7 0K, 3 cracked. 55." OK 0K OK All cracked. K 7 0K, 3 cracked. 0K Do. All cracked All cracked All cracked Do.

From the above tabulation it can be seen that plastic closures made from the improved molding compositions such as compositions B, D and E, show greatly improved impact resistance over plastic closures made from the standard phenolic compositions which are currently commercially used.

Bleed test The bleed test is conducted in conjunction with the standard absorption test wherein sets of closures are' weighed before and after a prolonged immersion. In the absorption test, one group of closures is immersed in distilled water whereas another group is immersed in a solution of equal volumes of distilled water and ethyl alcohol. The containers containing the immersed closures are placed in an oven at 122 F. for a period of seven days, after which the caps are removed and weighed to determine the gain in weight due to absorption. At this time, the bleed test is conducted in order to determine the discoloration etfect of the closures on the solution. The light transmission is measured by a standard electrophotometer. According to tests accepted by the plastic industry, the transmission must not be less than which corresponds to a very light amber color. Tests conducted on plastic closures of my improved composition indicate excellentresults. For example, plastic closures made from moldi sQmnQsiti9n..B.hQvsd. transmission in water and 91% transmission in wateralcohol.

In addition to the improved,impactresistancc and improved bleed test results, plastic closures made from the molding compositions have improved resilience and dimensional stability. Moreover, the closures may be satisfactorily molded with a minimum of cure, time required, without staining the molds.

Modifications-may be resorted to .Within the spirit and scope of theappended claims.

This application is a continuation-in-part of my copending'application Serial No. 413,707, filed March 2, 1954, now abandoned, entitled lylolding Composition for Plastic Closures.

I claim: i

1. A molding composition for plastic closures, each lparts-by weight of said molding composition comprising 42-48 parts of an uncured phenol-formaldehyde resin, 28-38 parts of woodfiour, -l0-20 parts of vulcanized rubber composition, -a small amount of carbon black and a small amount of stearate compound selected from the group consisting of zinc stearate and calcium stearate, each 100 parts by weight of said rubber composition comprising 12-70 parts of butadiene-styrenecopolymer rubber, and 8-30 parts sulfur,-said composition on combustion analysis yielding 1-35 parts ash content per 100 parts of rubber composition.

2. A molding composition for plastic closures, each 100 parts by weight of said molding composition comprising 48 parts of an uncured phenol-formaldehyde resin, 38 parts of woodflour, 1 0 parts of vulcanized rubber composition, a small amount of carbon blackand a small amount of stearate compound selected from the group consisting of zinc stearate and calcium stearate,

.each 100 parts by Weight of said rubber composition comprising 12-70 parts of butadiene-styr ene copolyrner rubber, and 8-30 parts sulfur, said compositiononcombustion analysis yielding l-3 5 parts ash content perparts of rubber composition.

'3 A m'oldingcoi'nposition for plastic closures, each 100 parts by weight of said molding composition comprising 48 parts of an uncured phenol-formaldehyde resin, 28 parts of woodfiour, 20 parts of vulcanized rubber composition, a small amount of carbon black and a small amount of stearate compound selected from the groupfconsisting of zinc stearate and calcium stearate, each 100 parts by weight of said rubber composition comprising 12-70 parts of butadiene-styrene cop'olymer rubber and 8-30 ipar ts. sulfur, said composition on combustion analysis yielding l-35 parts ash content per 100 parts of rubbercomposition.

4. A molding composition for plastic closures, each 100 parts by weight ofsaid molding composition comprising 48 parts of an uncured phenol-formaldehyde resin, 33 parts of woodflour, 15 parts of vulcanized rubber composition, a small amount of carbon black and a small amount of stearate compound selected from the group consisting of Zinc stearate and calcium stearate, each 100;parts by weight of said rubber composition comprising 12-70 parts of butadiene-styrene eopolymer rubben a'nd 8-30 parts sulfur, said composition on combustion analysis yielding 1-35 parts ash content per 100 parts of rubber composition. 7

5. A. molding composition for plastic closures, each 100 parts by weigh'tof said molding composition comprising 42 partsof an -uncured phenol-formaldehyde resin, 34'parts of woodflour, 20 parts of vulcanized rubber composition, a small-amount of carbon black and a smallam'ount .of stearate compound selected from the group consisting of zincrstearate and calcium stearate,

each 100 parts byweight of said-rubber composition comprising 12-70 parts of butadiene-styrenecopolymer rubher, and 8-30 parts sulfur, said composition on combustion analysis yielding 1-35 parts ash contentper 100 partsof rubber composition.

No references cited. 

1. A MOLDING COMPOSITION FOR PLASTIC CLOSURES, EACH 100 PARTS BY WEIGHT OF SAID MOLDING COMPOSITION COMPRISING 42-48 PARTS OF AN UNCURED PHENOL-FORMALDEHYDE RESIN, 28-38 PARTS OF WOODFLOUR, 10-20 PARTS OF VULCANIZED RUBBER COMPOSITION, A SMALL AMOUNT OF CARBON BLACK AND A SMALL AMOUNT OF STEARATE COMPOUND SELECTED FROM THE GROUP CONSISTING OF ZINC STEARATE AND CALCIUM STEARATE, EACH 100 PARTS BY WEIGHT OF SAID RUBBER COMPOSITION COMPRISING 12-70 PARTS OF BUTADIENE-STYRENE COPOLYMER RUBBER, AND 8-30 PARTS SULFUR, SAID COMPOSITION ON COMBUSTION ANALYSIS YEILDING 1-35 PARTS ASH CONTENT PER 100 PARTS OF RUBBER COMPOSITION. 